1. Field of the Invention
This invention relates to fluid power safety devices known as "No Tie Down" devices and circuits, whereby actuation of a hazardous machine cannot be accomplished unless the operator thereof actuates two hand valves or switches in a near-simultaneous fashion.
2. Description of the Prior Art
The conventional manner of achieving no tie down characteristics has been to arrange a system of valves controlled by a pulse valve, the arrangement being known as a no tie down circuit. Such a circuit will ensure that a pressurized output can be obtained if and only if two hand valves are actuated and held within a predetermined small time interval. This procedure has obvious beneficial application in controlling hazardous machinery, since proper mounting of the hand valves can make it impossible for the operator thereof to have either of his hands in dangerous areas during actuation. Beyond the desirability of the no tie down process, there is the fact that it is now law in the United States that any hazardous industrial machinery must be so equipped.
The problem with the present arrangement is the complexity of no tie down circuits, and, consequently, their high cost and increased probability of failure.